Answer: 24 hours
Step-by-step explanation:
Given : A drill can dig through rock at a rate of [tex]2\dfrac{1}{2}[/tex] inches per hour.
i.e. Speed= [tex]2\dfrac{1}{2}=\dfrac{5}{2}[/tex] inches per hour.
Formula we use here is : [tex]\text{Time}=\dfrac{\text{Depth}}{\text{Speed}}[/tex]
We assume that it maintains this rate of digging.
Since 1 feet = 12 inches
Depth to dig = [tex]5\ \text{feet}=5\times12=60\text{ inches}[/tex]
The number of hours it will take for the drill to reach 5 feet below the rocky surface will be
[tex]\text{Time}=\dfrac{60}{\dfrac{5}{2}}=\dfrac{60\times2}{5}=24[/tex]
Hence, it will take 24 hours for the drill to reach five feet below the rocky surface.
